The following represent the major defined objectives for this award: 1. Isolation and characterization of human thymocyte-specific and peripheral T lymphocyte membrane antigens detected by serologically defined nonhuman primate and rabbit antisera. 2. Production and serological characterization of other rabbit and simian antisera capable of defining membrane antigens of human T and B cells or other subpopulations of human lymphocytes. 3. In vivo and in vitro studies on the effects of T and B cell specific primate antisera on human and simian lymphocyte functions. 4. Expand the immunologic studies on experimentally produced (thymectomized and irradiated) T cell deficient chimpanzees. BIBLIOGRAPHIC REFERENCES: Metzgar, Richard S., Mohanakumar, T. and Miller, Donald S.: Membrane bound immunoglobulins on human leukemic cells: Evidence for humoral immune responses of patients to leukemia associated antigens, (J. Clin. Invest. 56: 331-338, 1975). T. Mohanakumar, Pauly, John L., Sokal, Joseph E. and Metzgar, Richard S.: Human leukemia-associated antigens: Detection of cells of established lymphoblastoid lines, (J. Immunology 115: No. 6, 1975).